1. Field of the Invention
This invention relates to ring resonators for lasers and especially to a decentered annular ring resonator using two waxicon beam reflectors.
2. Description of the Prior Art
The Decentered Annular Ring Resonator (DARR) has often been considered as a candidate resonator for extracting power from an annular gain region of an associated laser. A typical DARR configuration is shown in FIG. 1. The DARR consists basically of two waxicons 18,20, one at each end of annular gain region, a scraper/feedback mirror train 14,22,24 in the compact leg of the resonator to provide the out-coupled beam 26 and the feedback beam 28. The power is extracted fom the annular gain region 12 by the collimated annular beam. The terminology "decentered" arises from the fact that the feedback beam is created by a decentered hole 16 in the scraper mirror.
The Achilles heel of the DARR is its sensitivity to small misalignments of the waxicon assemblies. A tilt of either waxicon introduces a cos .phi. (where .phi. is the aximuthal angular coordinate) phase error in the outcoupled beam. Such phase errors degrade the focusability of the output beam, i.e., the peak far-field irradiance is seriously degraded by near-field phase errors of the form cos .phi.. The sensitivity of the DARR to waxicon tilt misalignment is so great that the DARR is impractical for many applications.